Disappointed customer

I am a loyal Game customer,I was then sent an online shopping voucher which I then went in store 2 redeem to do my shopping.When I got to the till the lady asked me to show it to the supervisor then she called someone else to confirm if they can cash it out.She then attempts a gift receipt which declined.I was then told I wasn’t the only or first customer who ended up not being able to use the voucher. Please advise why are we made fools with this kind of **** if I can call it that.I am very disappointed with this whole thing😡,we are being made fools.🚮